1. Field of the Invention
The present invention relates to an optical device that can efficiently apply light to a light modulation device (display device) such as a liquid crystal display panel and can be miniaturized, as well as to a display apparatus having such an optical device.
2. Description of the Related Art
Recently, display apparatuses such as a projector apparatus, a television receiver, and a computer display that use an optical device such as a liquid crystal display panel that is a light modulation device called a light bulb have spread in a variety of fields.
In such display apparatuses using a liquid crystal display panel or the like, a light beam that is emitted from a light source having ametal halide lamp, a halogen lamp, or the like is separated into beams of the three primary colors, which are input to a liquid crystal display panel having color filters (R, G, and B) that are provided for the respective colors to improve the color purity. The three beams are modulated by the liquid crystal display panel in accordance with an input video signal and then combined with each other to generate color video signal light, which is projected onto a screen via a projection lens in an enlarged manner.
In the above type of optical system, it is required that a light beam that is emitted from the light source be applied to the liquid crystal display panel efficiently and uniformly. However, the light-emitting surface of the light source has some surface area and hence it is difficult to use the light source as an ideal point light source; a light beam emitted from a real light source has a large divergence angle. Therefore, it is difficult to apply efficiently a light beam emitted from the light source to the liquid crystal display panel.
One generally known method of efficiently applying a light beam that is emitted from a light source and has a large divergence angle to a liquid crystal display panel is such that a light beam to be input to the liquid crystal display panel is converged and uniformized in illuminance profile by using, for example, a lens array in which a number of small lenses are arranged in matrix form.
A general example using such a lens array will be described below with reference to FIG. 1. In a light source 510, a metal halide lamp 510a, for example, is disposed at the focal position of a paraboloid mirror, whereby a light beam that is approximately parallel with the optical axis of the paraboloid mirror is output from its opening. Unnecessary components in the infrared (IR) range and the ultraviolet (UV) range of the light beam output from the light source 510 are interrupted by a UV/IR-cutting filter 511 and only the effective light beam is introduced to a downstream first optical block 501.
The first optical block 501 is constituted of optical elements including a first lens array 512 in which a plurality of convex cell lenses 512a each having an outer shape that is approximately similar (equal in aspect ratio) to the effective apertures of liquid crystal display panels 517, 521, and 527 as light modulation devices (light spatial modulation devices) are arranged in matrix form.
A second lens array 513 of a second optical block 502 that is disposed downstream of the first optical block 501 is formed with a plurality of convex cell lenses 513a on the incidence side and with a single convex surface 513b as a first converging component on the exit side.
Dichroic mirrors 514 and 519 for separating a light beam that has been emitted from the light source 510 into beams of red, green, and blue are disposed between the second lens array 513 and the effective apertures of the liquid crystal display panels 517, 521, and 527.
In the example of FIG. 1, a red beam R is reflected and a green beam G and a blue beam B are transmitted by the dichroic mirror 514. The red beam R reflected by the dichroic mirror 514 is bent in traveling direction by 90.degree. by a mirror 515, converged by a condenser lens 516, and finally input to the red liquid crystal display panel 517.
On the other hand, the green beam G and the blue beam B that have passed through the dichroic mirror 514 are separated from each other by a dichroic mirror 519. That is, the green beam G is reflected and bent in traveling direction by 90.degree. by the dichroic mirror 519 and then introduced to the green liquid crystal display panel 521 via a condenser lens 520. The blue beamB passes through the dichroic mirror 519 (goes straight) and is then introduced to the blue liquid crystal display panel 527 via relay lenses 522 and 524, a condenser lens 526, and mirrors 523 and 525.
A polarizing plate (not shown) for polarizing incident light in a predetermined direction is disposed on the incidence side of each of the liquid crystal display panels 517, 521, and 527 and a polarizing plate (not shown) that transmits only a component having a prescribed polarization plane of exit light is disposed downstream of each of the liquid crystal display panels 517, 521, and 527 so that the light intensity is modulated in accordance with the voltage of a liquid crystal driving circuit.
The beams of the respective colors that have been modulated by the liquid crystal display panels 517, 521, and 527 are combined with each other by a dichroic prism 518 as a light composing means. In the dichroic prism 518, the red beam R and the blue beam B are reflected by respective reflection surfaces 518a and 518b so as to be directed to a projection lens 530. The green beam G passes through the reflection surfaces 518a and 518b. As a result, the R, G, and B beams are combined together so as to travel along the same optical axis, and are then projected onto a screen (not shown) by the projection lens 530 in an enlarged manner.
Next, the optical system including the respective lens arrays 512 and 513 of the first optical block 501 and the second optical block 502 will be described in more detail with reference to FIGS. 2, 3, and 4A-4B.
FIG. 2 shows an example of how beams are formed mainly by the optical characteristic of the first optical block 501. A god light beam L emitted from the light source is divided by the cell lenses 512a of the first lens array 512 and, after exiting from the first optical block 501, forms images corresponding to the respective cell lenses 512a of the first lens array 512 in the vicinity of the second optical block 502.
Then, the beams are introduced to the condenser lens 520 as a second converging component by the first converging component 513b.
At this time, image points of cells in a peripheral portion of the first lens array 512 become large-angle-of-view object points of the condenser lens 520 as the second converging component. In this manner, images formed in the vicinity of the second optical block 502 by the respective cell lenses 512a of the first lens array 512 are re-imaged in the vicinity of an entrance pupil E of the projection lens 530 by the condenser lens 520 as the second converging component.
FIG. 3 shows an example of how a light beams are formed mainly by the second optical block 502. A divergence angle .theta. of a beam that can be captured from the above-described illumination system can be controlled by properly setting the external dimensions of each cell lens 513a of the second lens array 513 and the interval between the first lens array 512 and the second lens array 513.
Beams thus captured within the divergence angle .theta. are introduced to the condenser lens 520 as the second converging component by the convex surface 513b as the first converging component, and applied, efficiently and uniformly, to the liquid crystal display panel 521 by a composite converging component that is a combination of the first and second converging components.
However, the above action causes the following problems. A beam that passes through a central portion of the convex surface 513b converges at position P1 that is close to the liquid crystal display panel 521, and a beam that passes through a peripheral portion of the convex surface 513b converges at position P2 that is close to the second lens array 513. That is, the imaging position shifts from the liquid crystal display panel 521 side to the second optical block 502 side as the beam passes through a portion of the convex surface 513b that is closer to its periphery.
A light beam that has been applied to, for example, the liquid crystal display panel 521 in the above manner is modulated by the liquid crystal display panel 521 having the polarizing plates on its upstream and downstream sides, and then input to a color composing element such as a dichroic prism 518.
The beam that enters the condenser lens 520 as the second converging component after passing through the convex surface 513b as the first converging component is a green beam G that has been separated halfway from a red beam R and a blue beam B by the optical elements such as the dichroic mirrors (not shown).
The dichroic prism 518 is formed by bonding together four prisms via reflection surfaces 518 and 518b that are thin films having a prescribed reflection characteristic.
The red light R, the green light G, and the blue light B are modulated by the respective liquid crystal display panels (only the green beam G is indicated by solid lines in FIG. 2) and enter the cross dichroic prism 518 from different directions as indicated by arrows.
While the green beam G that has been modulated by the liquid crystal display panel 521 simply passes through the dichroic prism 518, the red light R and the blue light B are reflected by the respective reflection surfaces 518a and 518b. In this manner, the R, G, and B beams are combined with each other by the cross dichroic prism 518 into color video signal light, which is input to the projection lens 530.
By disposing the lens arrays 512 and 513 having the convex lenses 512a and 513a, respectively, that are arranged in matrix form downstream of the light source in the above-described manner, a light beam emitted from the light source can be applied to the effective aperture of, for example, the liquid crystal panel 521 more efficiently with a higher degree of uniformity than in a case where only a condenser lens is provided.
However, in the above example using the first optical block 501 and the second optical block 502, each of the first lens array 512 and the second lens array 513 has lens cells having exactly the same shape that are arranged in matrix form.
A first problem of the case of using the above-configured lens arrays is as follows. As shown in FIG. 2, the imaging positions and the aberrations of the respective cell lenses 512a of the first lens array 512 are exactly the same. Beams imaged by the respective cell lenses 512a of the first lens array 512 are introduced to the condenser lens 520 as the second converging component by the convex surface 513b as the first converging component. As shown in broken lines and solid lines in FIG. 2, the beams enter the condenser lens 520 at different angles. Therefore, as shown in FIGS. 2 and 4A, since the beams are influenced by the off-axis aberrations of the condenser lens 520, the imaging performance of the beams becomes non-uniform in the vicinity of the entrance pupil E as indicated by regions AR1 and AR2, to cause loss and unevenness in light quantity.
A second problem is as follows. As shown in FIG. 3, the cell lenses 513a of the second lens array 513 act on respective beams in different ranges of a light beam that is imaged in the vicinity of the liquid crystal panel 521 by the converging component that is a combination of the convex surface 513b as the first converging component and the condenser lens 520 as the second converging component. As a result, as shown in FIGS. 3 and 4B, the beams passing through the respective cell lenses 513a of the second lens array 513 are influenced differently by the aberrations of the composite converging component, and their imaging performance in the vicinity of, for example, the liquid crystal display panel 521, to cause loss and unevenness in light quantity.
A light beam emitted from an ordinary light source has two orthogonal polarization planes and polarization components having those polarization planes are generally called a P-polarization component (hereinafter referred to as a P wave) and an S-polarization component (hereinafter referred to as an S wave) In this type of display apparatus, a light beam emitted from the light source is applied to a polarizing means provided upstream of the liquid crystal display panel, to thereby extract only a P wave or an S depending on the type of polarizing plate disposed in front of the liquid crystal display panel.
A polarizing beam splitter (hereinafter abbreviated as PBS) is used as a means for producing only a P or S wave. For example, a light beam having random polarization (P+S waves) is input, at a predetermined angle, to a PBS that is provided in a prism, and a P wave is transmitted while an S wave is reflected. Both of the P and S waves are returned to parallel beams by refracting those by end faces of the prism, and only the S wave, for example, is caused to pass through a (1/2).lambda. plate so as to be converted to a P wave. Alternatively, the S wave is refracted by an end face of the prism or reflected by a reflecting means such as a mirror so as to become parallel with the traveling direction of the P wave that has passed through the PBS, and then the S wave is input to a (1/2).lambda. plate so as to be converted to a P wave.
The former type of optical block is a symmetrical one-unit device and the latter type of optical block is a symmetrical one-unit or two-unit device.
FIG. 5 shows an example configuration and optical paths of a conventional polarizing means.
A light source 530 is a halogen lamp, a metal halide lamp, or the like. A light beam emitted from the light source 530 is input to an optical block 540, whereby only P waves, for example, are caused to enter a liquid crystal display panel (not shown) The optical block 540 is formed by bonding together a plurality of prisms 540a-540f made of glass, for example. PBSs 542 are provided between the prisms 540b and 540c and between the prisms 540d and 540e. Wave plates 543 are provided in front of the respective prisms 540a and 540f. Optical paths of P+S waves emitted from the light source 530 are indicated by solid arrows, optical paths of P waves separated by the optical block 540 are indicated by blanked arrows, and optical paths of S waves are indicated by hatched arrows.
P waves and S waves emitted from the light source 530 are separated from each other by the PBSs 542. The P waves simply pass through the PBSs 542 and reach the liquid crystal panel side. The S waves are reflected by the PBSs 542, reflected forward by the prisms 540a and 540f, and then converted by the wave plates 543 to P waves, which enter the liquid crystal display panel. That is, only the P waves are output from the prisms 540c and 540d and the front surfaces of the wave plates 543.
In this manner, the optical block 540 causes only one of the P wave and S wave that are emitted from the light source 530 to enter the liquid crystal display panel (not shown).
Incidentally, where the optical block 540 is not used, the opening of the light source 530 is similar to the effective area of the liquid crystal display panel and it is difficult to apply light uniformly to also side portions of a liquid crystal display panel for forming a horizontally long image of an aspect ratio 16:9, for example (the illuminance profile does not become uniform).
It is difficult to efficiently illuminate a liquid crystal display panel with a light beam emitted from a lamp light source and having a large divergence angle. In a conventional technique for solving this problem, light reaching a liquid crystal display panel is increased while the illuminance profile is uniformized by using such an optical means as a multi-lens array in which a number of small lenses are arranged.
For example, as shown in FIG. 6, aplurality of convex lenses 544a of a multi-lens array 544 are each formed so as to be similar (equal in aspect ratio) to the effective aperture of a liquid crystal display panel as a light modulation device, and are arranged in matrix form. The convex lenses 544a of the flat multi-lens array 544 provided on the light source (not shown) side are formed so as to be opposed to respective convex lenses 545a of a multi-lens array 545. A light beam emitted from the light source (not shown) is applied to the effective aperture of a liquid crystal display panel.
A light beam emitted from the light source of a liquid crystal projector apparatus enters the multi-lens array 544 and is then focused on the convex lenses 545a of the multi-lens array 545 by the respective convex lenses 544a. The convex lenses 545a, an exit-side convex lens 545b, and a condenser lens 546 re-image the images formed by the respective convex lenses 544a on a liquid crystal panel 547 so as to be superimposed one on another.
FIG. 6 shows only the optical path of a green beam G by solid lines. A red beam R and a blue beam B are similarly modulated by red and blue liquid crystal display panels (not shown) and applied to a cross dichroic prism 548 from different directions as indicated by arrows.
The red beam R and the blue beam B that have been modulated by the respective liquid crystal display panels are reflected by respective reflection surfaces 548a and 548b of the dichroic prism (also called a cross prism) 548 toward a projection lens (not shown) side. The green beam G passes through the reflection surfaces 548a and 548b. Therefore, the R, G, and B beams are combined by the dichroic prism 548 so as to go along the single optical axis and enter the projection lens.
By disposing the multi-lens arrays 544 and 545 having the convex lenses 544a and 545a, respectively, that are arranged in matrix form downstream of the light source in the above-described manner, a light beam emitted from the light source can be applied to the effective aperture of, for example, the liquid crystal panel 547 more efficiently with a higher degree of uniformity than in a case where only the condenser lens 546 is provided.
If the optical block 540 is disposed in front of the opening of the light source 530 and the multi-lens arrays 544 and 545 are disposed in front of the aperture of the optical block 540 as shown in FIG. 7, a light beam that is output from the light source 530 can be utilized more efficiently than in the cases of FIGS. 5 and 6.
However, since the incidence-side portion of the optical block 540 of FIG. 7 has approximately the same size as the opening of the light source 530, the exit-side portion of the optical block 540 is made larger than the light source 530. Therefore, not only is a large space needed to accommodate the optical block 540 but also the cost increases.
Where only the multi-lens arrays 544 and 545 are provided as shown in FIG. 6, a randomly polarized light beam as emitted from the light source is input to the polarizing plate. Since about 60% of the total light quantity is interrupted, the efficiency of utilization of the light source is not high.
Even where the optical block 540 and the multi-lens arrays 544 and 545 are combined as shown in FIG. 7, the multi-lens arrays 544 and 545 are made as large as the exit-side aperture of the optical block 540, to cause a problem that the optical path length from the multi-lens array 545 to the liquid crystal panel 547 is increased.
Recently, to solve the above problems, for example, an optical device for a display apparatus as shown in FIG. 8 has been proposed. In an optical block used in this optical device, its incidence-side portion and exit-side portion can be formed in approximately the same size as the opening of a light source. Further, the optical block can be made thin. Therefore, this optical device enables space saving and weight reduction.
The optical device of FIG. 8 is composed of a multi-lens array 512 in which a plurality of convex lenses 512a each having an external shape that is approximately similar (i.e., equal in aspect ratio) to the effective apertures of liquid crystal display panels 517, 521, and 526 as light spatial modulation devices are arranged in matrix form, an optical block 501 that is constituted of prescribed optical parts, and a multi-lens array 513 that is disposed in front of the optical block 501 and in which a plurality of convex lenses 513a are formed.
The optical block 501 is formed by bonding together a plurality of prisms, and beams focused by the multi-lens array 512 are input to predetermined prisms of the optical block 501. The randomly polarized beams (P+S waves) are polarized into P-polarization (or S-polarization) beams by the optical block 501, pass through or are reflected by the multi-lens array 513 and various optical elements such as dichroic mirrors, and are finally input to the liquid crystal display panels 517, 521, and 526 in a state that the beams are separated into R, G, and B beams.
That is, the multi-lens arrays 512 and 513 and the optical block 501 allow a light beam emitted from the light source 506 to be applied to the effective apertures of the respective liquid crystal display panels 517, 521, and 526 efficiently and uniformly.
The multi-lens array 513, which is disposed downstream of the optical block 501, is formed with a plurality of convex lenses 513a on the incidence side (the side opposed to the optical block 501) and with a single convex surface as a condenser lens on the exit side (liquid crystal display panel side). Dichroic mirrors 514 and 519 for separating a light beam emitted from the light source 506 into R, G, and B beams are disposed between the multi-lens array 513 and the effective apertures of the liquid crystal display panels 517, 521, and 526.
The optical block 501 will be described below with reference to FIGS. 9 and 10. FIG. 9 is a perspective view, as viewed from the front side, showing an appearance of the optical block 501, and FIG. 10 is a top plan view showing part of the optical block 501 in an enlarged manner.
For example, the optical block 501 is formed by bonding together triangular prisms 502a and 502b and parallelogrammic prisms 503a and 503b. Randomly polarized beams (P+S waves) that have been emitted from the light source 506 and passed through the multi-lens array 512 are input to the optical block 501 from a direction indicated by a solid arrow, and only P waves, for example, are output from the respective prisms 503a and 503b as indicated by blanked arrows.
The exit-side slope surface of each prism 503a is provided with a PBS 504 that, for example, reflects an S wave and transmits a P wave. A P wave that has passed through the PBS 504 is output forward from the front surface of the prism 503b or 502b.
The slope surface of each prism 503a opposed to the PBS 504 is provided with a mirror 505 that reflects forward an S wave that has been reflected by the PBS 504. A (1/2).lambda. plate 506 indicated by hatching is provided on the front surface of each prism 503a to convert an S wave that has been reflected by the PBS 504 to a P wave and output it forward.
That is, the prisms 503a serve as incidence portions of the optical block 501, and beams that have entered the prisms 503a are polarized by the PBSs 504 and output forward from the prisms 502b, 503a, and 503b. The prisms 503a are provided in a number corresponding to the number of convex lenses 512a of the multi-lens array 512 or convex lenses 513a of the multi-lens array 513.
The optical block 501 that is composed of the prisms, PBSs 504, mirrors 505, etc. makes it possible to convert input randomly polarized beams (P+S waves) to P waves and output the P waves. Further, the incidence-side area of the optical block 501 is made equal to its exit-side area. In addition, since the optical block 501 can be made thinner than conventional ones, the space for accommodating the optical block 501 can be saved.
In the optical means shown in FIG. 6 using only the multi-lens arrays, because of their principle of operation, it is appropriate from the viewpoint of light utilization efficiency to set the focal length of the convex lenses 544a and 545a of the multilens arrays 544 and 545 approximately equal to the air-converted distance between the multi-lens arrays 544 and 545.
However, in the optical device for a display apparatus shown in FIG. 8 in which the multi-lens arrays 512 and 513 and the optical block 501 are combined, beams output from the multi-lens arrays 512 pass through the optical block 501 before reaching the multi-lens array 513. Therefore, as shown in FIG. 10, there is a difference in air-converted distance between an optical path 551 of beams that reach the multi-lens array 513 after passing through the PBSs 504 and an optical path 552 of beams that reach the multi-lens array 513 after being reflected by the PBSs 504 and the mirrors 505 and passing through the (1/2).lambda. plates 506.
FIGS. 11A and 11B compare the optical paths 551 and 552 having such a difference with regard to the imaging relationship between the multi-lens array 512 and the liquid crystal panel 517.
In FIGS. 11A and 11B, with an assumption that a convex lens 512a of the multi-lens array 512 is an image point IM1, the image point IM1 is re-imaged on the liquid crystal display panel 517 as an image point IM2 by the multi-lens array 513 and the condenser lens 516.
All the lenses of the conventional multi-lens array 513 have the same focal length that is equal to the air-converted distance of the optical path 551. Therefore, in the case of the optical path 552, because of the difference in air-converted distance from the optical path 551 that occurs in the optical block 501, an image on the liquid crystal display panel 517 is in a defocused state PX. This is a factor of decreasing the quantity of light that passes through the liquid crystal display panel 517 and in turn lowering the light utilization efficiency of the light source.